Substantial research is being conducted in connection with MIMO OFDM to combine MIMO techniques with multicarrier (MC) schemes, it being understood that OFDM is but a special form of MC-CDMA. MIMO MC-CDMA is also being considered for the “4G” radio access scheme to provide the target data rate of the 4G system. In order to improve the system throughput in MIMO MC-CDMA, multicode transmission techniques are preferably incorporated into the system to provide the same information data rate as MIMO OFDM.
In order to provide the target data rate of the “4G” system, multicode transmission with MIMO technique is preferably combined simultaneously with MC-CDMA. However, under a multipath fading channel, MIMO Multicode MC-CDMA is problematic, because inherent in it are two interferences, namely, one from inter-code interference between the multicode under the multipath fading channel, and a second from inter-antenna interference caused from an independent stream of different antennas.
In mitigating the inter-code interference and inter-antenna interference, it is first noted that a relatively simple Bell Labs Space Time (BLAST) algorithm may be used in a MIMO (non-multicode) MC-CDMA system to distinguish the different TX-antenna streams, chip-by-chip. The aforementioned two interferences then provide the error floor performance. BLAST is described in further detail in U.S. Pat. No. 6,097,771 filed on Jul. 1, 1996, on behalf of Gerard J. Foschini and entitled “Wireless communications system having a layered space-time architecture employing multi-element antennas”, in an article published in Bell Labs Tech. J., pages 41-59, Autumn 1996 by Gerard J. Foschini which was entitled “Layered space-time architecture for wireless communication in a fading environment when using multi-element antennas”, in EP 0 817 401 A2, filed on Jul. 1, 1996, on behalf of Gerard J. Foschini and entitled “Wireless communications system having a layered space-time rchitecture employing multi-element antennas”, and in EP 0 951 091 A2, filed on Apr. 15, 1998, on behalf of Gerard J. Foschini and Glenn D. Golden, and entitled “Wireless communications system having a space-time architecture employing multi-element antennas at both the transmitter and the receiver”, all of which are incorporated herein by reference in their respective entireties.
Second, it is noted that, in contrast to MIMO MC-CDMA, in MIMO OFDM systems, there is only one interference from the independent stream of the different antennas, and the simple BLAST algorithm is effective for mitigating this inter-antenna interference.
Third, because MIMO OFDM has no spreading code, multicode is used, and as a consequence, there is no Multiple Access Interference (MAI) existing in MIMO OFDM systems. However, in a MIMO MC-CDMA system, additional interference is provided by the MAI caused by inter-code non-orthogonality.
In light of the foregoing, it is apparent that there is a need for a system and method which may be utilized to enhance the performance of the MIMO Multicode MC-CDMA system under a multipath fading channel. Such a system and method should, among other things, simultaneously mitigate both inter-code interference and inter-antenna interference.